/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMesh3.h
Split an edge of the mesh by inserting a vertex. This creates a new triangle on either side of the edge (ie a 2-4 split). If the original edge had vertices [a,b], with triangles t0=[a,b,c] and t1=[b,a,d], then the split inserts new vertex f. After the split t0=[a,f,c] and t1=[f,a,d], and we have t2=[f,b,c] and t3=[f,d,b] (it's best to draw it out on paper...)
Ok on success, or enum value indicates why operation cannot be applied. Mesh remains unmodified on error.
virtual [EMeshResult](API\Runtime\GeometryCore\UE__Geometry__EMeshResult) SplitEdge ( int EdgeAB, [FEdgeSplitInfo](API\Runtime\GeometryCore\DynamicMesh\FDynamicMesh3\FEdgeSplitInfo) & SplitInfo, double SplitParameterT )